Epidemiology

Question 1

what is prevalence

Answer 1

the number of existing cases in a population at a designated time

Question 2

what is incidence

Answer 2

the number of new cases

Question 3

relationship between prevalence and incidence

Answer 3

prevalence = incidence x average disease duration

Question 4

name the three types of population pyramid

Answer 4

-spike - high birth rate, high death rate
-wedge - high birth rate, low death rate, high growth rate
-barrel - low birth rate, low death rate

Question 5

what is infant mortality rate

Answer 5

no. of deaths of infants aged 0-1years/no. live births

Question 6

what is a total period fertility rate (TPFR)

Answer 6

the average number of children that would be born to a woman over her lifetime

Question 7

define life expectancy

Answer 7

the number of years a baby born today can be expected to live if it experienced the current age-specific mortality rates

Question 8

what is healthy life expectancy

Answer 8

expected years of life in good or fairly good general health

Question 9

what is the PYLL index

Answer 9

potential years of life lost
-a measure of the relative impact of various diseases and lethal forces on society
(the number of years of life lost when a person dies prematurely)

Question 10

what is dependency ratio

Answer 10

a demographic measure of the ratio of the number of dependents to the total working age population in a country or region

Question 11

how do you calculate dependency ratio

Answer 11

under 15 plus over 65 years/population ages 15-64 years

Question 12

what’s a cross sectional study

Answer 12

estimate frequency or outcome at a particular point in time
-descriptive or analytical

Question 13

why do a cross sectional study?

Answer 13

-health service planning - prevalence of specific outcome in a defined population at a point in time
-useful for assessing burden of disease and planning preventative and curative services
-not useful for rare diseases
-generate hypotheses about causes
(these studies prove association not causation)

Question 14

survey sampling

Answer 14

-can make statements about the population by asking a (small) sample
-a well taken sample is (almost) as informative as a complete census
-sampling is a feature of all research designs

Question 15

what is simple random sampling

Answer 15

-list the group
-generate random numbers
-contact selected individuals
-collect data

Question 16

what bias in cross-sectional studies

Answer 16

-selection bias (characteristics of those taking part vs those not taking part)
-information bias (recall bias)

Question 17

advantages of cross sectional

Answer 17

-easy and economical
-provides important information on the distribution and burden of exposures and outcomes - health service planning
-can be used as the first step in the study of a possible exposure-outcome relationship

Question 18

weaknesses of cross sectional

Answer 18

-limited value for investigating aetiological relationships
-can be difficult to establish the time-sequence of events, the exposure may have occurred as a result of the outcome (reverse causality)
-not good for rare diseases
-selection bias (characteristics of those taking part/not taking part)
-recall bias
-could generate hypotheses about causes

Question 19

what is an ecological study

Answer 19

observational study with populations or groups (instead of individuals) being unit of observation

Question 20

what are the uses of an ecological study

Answer 20

-described association at group level
-quick and cheap - routine data
-generates hypotheses - first step
-some risk factors may not easily be measurable at an individual level

Question 21

what is ecological fallacy

Answer 21

-ecological studies enable us to make ecological inferences about effects at the group-level
-they do not enable us to make inferences about individual risks
-an attempt to infer from the ecological level to the individual level is often called an ecological fallacy

Question 22

purpose of randomised control trials

Answer 22

-minimise selection bias
-minimise confounding
-if participants are blind to treatment allocation then reporting bias is minimised
-if investigators are blind to allocation then observer bias is minimised
-provides powerful evidence of a causal relationship between the intervention and the outcome

Question 23

what is incidence risk

Answer 23

the number of new cases in interval/population initially at risk

Question 24

what is incidence rate

Answer 24

the number of new cases/total person-time at risk

Question 25

what is incidence rate good for

Answer 25

dynamic populations

Question 26

what is incidence risk good for

Answer 26

static populations

Question 27

what is annual incidence

Answer 27

counts the deaths over a calendar year

Question 28

what is cumulative incidence

Answer 28

frequency of new cases over a specified period

Question 29

what to consider when deciding if risk factor and disease is causal (10 marks)

Answer 29

-consider relative risk, hazard ratio and odds ratio to determine strength of association -attributable risk -define causation and association -consider that aetiology of chronic disease is often difficult to determine -some exposures may cause more than one outcome -outcomes may be due to multiple exposures or continual exposure over time -causes may differ by individual -probabilistic causation is when causal factor increases the chance of disease -a sufficient cause is a complete causal mechanism that always produces disease

Question 30

case control main features, advantages and disadvantages (10 marks)

Answer 30

-measure exposure in cases vs controls -select (diseased) cases and (undiseased) controls -use odds ratio to interpret results -selection bias can occur as people who participate are only those who are eligible -observer bias can occur if knowledge of case/control status -same with participant bias -there can be rare outcomes -time varying exposures -can assess multiple exposures -there wouldn't be any recall bias -can prove a good causal relationship between exposure and outcome

Question 31

advantages of case-control studies

Answer 31

-no recall bias -can show rare outcomes (from rare diseases) -can look at multiple exposures/risk factors simultaneously -time varying exposures -quick, inexpensive and easy -useful initial studies to establish an association

Question 32

ecological fallacy 6 marker

Answer 32

-can happen in ecological studies -define ecological studies -ecological fallacy occurs when a researcher attempts to infer from the ecological level to the individual level -ecological studies do not enable us to make inferences about individual risks -there are complex associations between disease and exposure -countries with high or low exposure differ systematically in many other ways

Question 33

what does it mean if p<0.05

Answer 33

reject chance -conclude real effect

Question 34

what does it mean if p>0.05

Answer 34

cannot exclude chance -cannot conclude there is real effect

Question 35

advantages of randomised control trials

Answer 35

-minimises selection bias and confounding -if participant blind to allocation then minimises reporter bias -if observer blind to allocation then minimises observer bias -multiple outcomes can be examined -incidence rate of outcome can be measured

Question 36

disadvantages of randomised control trials

Answer 36

-very time consuming - trials can take years -recruitment is difficult and time consuming -impossible to do interventional trials sometimes -expensive

Question 37

advantages of cohort studies

Answer 37

-temporality - exposure status defined before outcome -can measure multiple outcomes from rare exposures -no recall bias -its possible to estimate all measures of incidence and effect

Question 37

disadvantages of cohort studies

Answer 37

-huge investment of time, human resources and financial resources -reproducibility is hard -loss to follow up - bias can be introduced which is difficult to control -requires large sample size -uncontrolled confounding variables -inefficient for rare diseases

Question 38

two types of information bias

Answer 38

reporter and observer

Question 39

reporting bias

Answer 39

-when subjects give an answer they think will please the investigator -when subjects conceal potentially embarrassing info -when subject with a specific health outcome report previous exposure with a different degree of accuracy to other subjects -when subject who have experienced a specific exposure report subsequent health events to a different degree of accuracy to others

Question 40

how can you avoid/minimise reporting bias

Answer 40

-use exposure data before outcome -objective data sources where possible -keep subjects unaware of association under study

Question 41

what is observer bias

Answer 41

-when accuracy of exposure data recorded by investigator differs (case control and cross sectional) -when accuracy of outcome data differs (cohort and intervention studies) -interviewer bias

Question 42

how do you avoid/minimise observer bias?

Answer 42

-the people who are responsible for classifying the outcome do not know the subjects' exposure category -blinding

Question 43

intention to treat

Answer 43

-compares outcomes for all randomised individuals (even if they stop taking treatment or drop out of study) -assesses the overall effect of assigning a subject to receive a particular intervention -analysis is the most important analysis as intervention and control groups compared as originally randomised -more likely to underestimate treatment effect (in randomised control trials lecture)

Question 44

short notes on incidence risk and rate (6 marks)

Answer 44

-incidence measures number of new cases in a group/population -incidence risk is number of new cases in an interval/population initially at risk -incidence risk is good for static populations -incidence rate is number of new cases /total person-time at risk -incidence rate measures the rate at which a new disease occured over a period of time -incidence rate is good for dynamic populations -annual incidence counts deaths over a calendar year -cumulative incidence is the frequency of new cases over a specified period

Question 45

Cluster sampling | 6 mark short notes

Answer 45

-cluster sampling involves dividing a population into clusters and then randomly selecting a sample of these clusters -clusters are randomised -there must be a lot of clusters to randomise to avoid unequal distribution -need increased sample size of individuals -subjects within a cluster may be different to subjects in other clusters so ideal is lots of small clusters -analysis more complicated as need to take account of cluster design -allocation concealment more difficult

Question 46

sampling frame | 6 mark short notes (only have 4 points rn)

Answer 46

-a sampling frame is a list of all the people forming a population from which a sample is taken -simple random sampling is when people in the group are allocated random numbers -the sampling frame comes from an initial group of interest from which individuals are selected -convenience samples are taken from a place that is convenient for that study

Question 47

SMR | short notes

Answer 47

-standard mortality ratio -a measure, expressed as either a ratio or percentage to quantify an increase or decrease in mortality in a study cohort compared to the general population -calculated from expected deaths in a study population -compares observed deaths with expected deaths -needs number of persons in each age group in population being studied -age specific death rates of general population by same age groups -observed deaths in study population